I heard that irises are different and unique for every person. According this link, probability of two irises having identical pattern is 1 in 10 to the 78th power. That's how iris scanners identify the identity of people. This technology is becoming very evident. So I ask, why are irises for each person different and unique?

  • $\begingroup$ What research have you done before asking this (interesting) question? Do you have evidence for, or have you "heard" that irises are unique (the latter, and lack of support for this statement can render this question off-topic). Can you support this statement? Do you think the same factors that control fingerprints can actually control the formation of the iris? $\endgroup$ Dec 18, 2014 at 2:39
  • $\begingroup$ @anongoodnurse I edited it.. I added evidence and links... and you're right, the same factors that control fingerprints probably don't control the formation of the iris...Thanks 4 the help! $\endgroup$
    – TanMath
    Dec 18, 2014 at 3:21

1 Answer 1


Iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina. The color of the iris gives the eye its color. In optical terms, the pupil is the eye's aperture and the iris is the diaphragm that serves as the aperture stop.

Color and structure of iris is greatly depended upon genetic links, but the patterns are not. Iris is developed by the prenatal(before birth) growth through a process of tight forming and folding of the tissue membrane.

The human iris begins to form during the third month of gestation. The structures creating its distinctive pattern are complete by the eighth month of gestation, but pigmentation continues into the first years after birth. The layers of the iris have both ectodermal and mesodermal embryological origin, consisting of (from back to front): a darkly pigmented epithelium; pupillary dilator and sphincter muscles; heavily vascularized stroma (connective tissue of interlacing ligaments containing melanocytes); and an anterior layer of chromataphores and melanocytes with a genetically determined density of melanin pigment granules. The combined effect is a visible pattern displaying various distinctive features such as arching ligaments, crypts, furrows, ridges, and a zigzag collarette. Iris colour is determined mainly by the density of the stroma and its melanin content, with blue irises resulting from an absence of pigment: longer wavelengths differentially penetrate while shorter wavelengths are reflected and scattered, a phenomenon resembling that which makes the sky blue. The heritability and ethnographic diversity of iris colour have long been studied, but until the present research, little attention had been paid to the achromatic pattern complexity and textural variability of the iris among individuals.


Iris Recognition vs. Retina Scanning

Iris and retinal scanning are ocular based biometric identifiers. Iris recognition uses a camera to capture image of the iris. Iris is the only internal organ visible from outside the body. Iris scanners can acquire an image of the eye from a distance of 3 to 10 inches. In retinal scanning, the device send a beam of light deep inside the eye to capture the image of retina, which is located on the back of the eye. retinal scanning is not widely used due to the intrusive methods used to capture the image.

Factors which enhance the iris scanning system,

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  • $\begingroup$ In the list titled "The Advantage of Iris Recognition", only the first two items are really biologically relevant. The other points are just advertising the technical features of some particular iris recognition system. $\endgroup$
    – augurar
    Dec 21, 2014 at 9:03
  • $\begingroup$ @augurar:Uniqueness of iris is described above the title you mentioned. Your point is right but I deliberately put it there for sharing some knowledge about background working of an iris scanner $\endgroup$ Dec 22, 2014 at 4:44

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